The present invention relates to apparatus and methods of semiconductor component packaging using interposers having an encapsulant fill control feature.
Semiconductor chips (or die) may be mounted to circuit boards or other electronic components in several ways. In a typical ball grid array (BGA) or fine ball grid array (FBGA) assembly 30 as shown in FIG. 1, a die 10 is attached to an interposer 22 having a plurality of conductive leads 18. The die may be attached to the interposer using, for example, strips of adhesive 12 (see FIG. 1), an adhesive layer (e.g. epoxy), eutectic bonding, or other suitable methods. Typically, the die 10 includes a plurality of conductive terminals 14 (or bond pads) that are electrically coupled to corresponding contact pads 16 on the interposer 22, thereby coupling the internal circuitry of the die 10 with the conductive leads 18. The conductive terminals 14 may be attached to the contact pads 16 in a variety of ways, including by bond wires 26 (see FIG. 1), solder reflow, conductive adhesives, or other suitable methods. The conductive leads 18 of the interposer 22 fan out from the die 10 and may be coupled to other electronic components, such as printed circuit boards, electronics modules, and the like. Solder balls 24 (FIG. 1) may be attached to the ends of the conductive leads 18 for attaching the interposer 22 to other electronic components. Electrical signals may then be transmitted from, for example, a circuit board through the conductive leads of the interposer to the die, and vice versa. Typical BGA assemblies are described, for example, in U.S. Pat. No. 5,086,558 to Grube et al, U.S. Pat. No. 5,258,648 to Lin, and U.S. Pat. No. 4,617,730, incorporated herein by reference.
As shown in FIG. 1, it is customary to provide one or more encapsulant layers 28 over the die 10, conductive terminals 14, contact pads 16, and other sensitive areas of the FBGA assembly 30. The encapsulant layer 28 hermetically seals the assembly, insulating and protecting the sensitive portions of the assembly from humidity, oxidation, and other harmful environmental elements. To reduce stresses that may be induced in the FBGA assembly 30 during thermal cycling, the encapsulant layer 28 may be composed of a soft, compliant polymeric material, such as silicone rubber or other castable elastomer having a relatively low modulus of elasticity. Alternate materials for the encapsulant material are described, for example, in U.S. Pat. No. 5,956,605 issued to Akram and Farnworth, incorporated herein by reference.
FIG. 2 is a side elevational cross-sectional view of the FBGA assembly 30 of FIG. 1 engaged with an encapsulant supplier 40 and a mold 42. The mold 42 includes a lower portion 46 and an upper portion 48. The lower and upper portions 46, 48 have inner surfaces that are spaced apart from the FBGA assembly 30 and are shaped to form the encapsulant layers 28 (FIG. 1). The encapsulant supplier 40 may be integrally formed with the upper half 48, as shown in FIG. 2, or may be a separate component.
After the FBGA assembly 30 is positioned within the mold 42, an encapsulant material 50 may be flowed through the encapsulant supplier 40. As it enters the mold 42, the flow of encapsulant material 50 may divide into a first stream 52 and a second stream 54. The first stream 52 may turn and flow over an outer portion of the die 10 between the die 10 and the upper half 48 of the mold 42. The second stream 54 may flow through an opening between the die 10 and the interposer 22 and into the space between the FBGA assembly 30 and the lower half 46 of the mold 42, surrounding the bond pads 14, the bond wires 26, and the contact pads 16.
Ideally, the first stream 52 substantially fills the space between the FBGA assembly 30 and the upper half 48 of the mold 42, and the second stream 54 substantially fills the space between the FBGA assembly 30 and the lower half 46 of the mold 42. After the fill procedure is complete, the encapsulant material 50 may be cured, such as by heating, cooling, or exposing the encapsulant material to curing agents, and the mold 42 may be removed. These operations are typically performed simultaneously on numerous FBGA assemblies that are joined together as a single unit along lateral edges of the interposers 22. After curing the encapsulant materials, the FBGA assemblies may be singulated into discrete packages.
One problem with the above-described FBGA assembly 30 is that the encapsulant material may not completely fill the space between the FBGA assembly 30 and the mold 42, particularly in the space surrounding the bond pads 14, the contact pads 16, and the bond wires 26. To provide good thermal conduction and mechanical strength, the space surrounding the bond pads 14, the contact pads 16, and the bond wires 26 should be void-free. Moisture or contaminants may collect in the voids, and may cause the die to come loose from the interposer, or may cause other malfunctions of the microelectronics package.
The present invention is directed to apparatus and methods of semiconductor component packaging using interposers having an encapsulant fill control feature. In one aspect, an interposer includes a substrate having a first surface proximate a region adapted to be occupied by a semiconductor component, and a fill control feature projecting from the first surface toward the region. The fill control feature is positioned at least partially between the region and the substrate and is sized to at least partially block an opening between a semiconductor component positioned within the region and the first surface. As an encapsulant material is flowed about the semiconductor component, the fill control feature at least partially diverts the encapsulant material from entering the opening. The at least partially diverted encapsulant material may then substantially surround the semiconductor component, after which the encapsulant material may substantially fill a space between the semiconductor component and the interposer. Because the fill control feature diverts a portion of the encapsulant material to cause the space surrounding the semiconductor component to substantially fill before the space between the semiconductor component and the interposer, the fill control feature may reduce the occurrence of voids and may otherwise improve the fill of the encapsulant material about the semiconductor component and the interposer.
In an alternate aspect, the semiconductor component may be attached to the interposer by a pair of adhesive strips, the opening being formed between the semiconductor component, the interposer, and the adhesive strips. Alternately, the semiconductor component may be attached to the interposer by a pair of conductive bumps, the opening being formed between the conductive bumps. In other aspects, the interposer may include a plurality of fill control features.